Technical Field
The present disclosure relates to a vehicle back door structure applied to a back door of a vehicle rear section.
Related Art
Structures for a back door are known in which a door upper end portion is attached to a vehicle body upper section by a door hinge, and, in a state in which a door lower end portion is locked, vertical direction intermediate portions of each of the two side portions of the door is biased toward a vehicle cabin outside by a damper (see, for example, Japanese Patent No. 5708428). Sometimes, in order to reduce weight, for example, a resin panel is employed in the back door (see, for example, Japanese Patent No. 5708428, Japanese Patent Application Laid-Open (JP-A) Nos. 2010-173348 and 2013-129265).
Here, the resin panel is more liable to deform than, for example, a metal panel, and so sometimes, from the viewpoint of securing a rigid fit, a bead portion is formed to both side portions of a resin door inner panel, and reinforcements for reinforcing the panel are fastened by bolts onto both side portions of the resin door inner panel (see, for example, paragraphs [0026], [0028], and FIG. 2 of Japanese Patent No. 5708428, and paragraphs [0002] to [0004] and FIG. 5 to FIG. 8 of JP-A No. 2010-173348. To briefly explain such structures, the bead portions on both side portions of the door inner panel extend in the door vertical direction and are formed with recessed shapes indented toward a vehicle cabin inside, and the reinforcements are disposed inside recessed portions of the bead portions and are fastened to the side portions of the door inner panel using bolts.
However, as illustrated in FIG. 6 to FIG. 8 of JP-A No. 2010-173348, for example, due to design considerations, locations of the door inner panel where the reinforcements are fastened using bolts are limited to locations that cannot be seen from the vehicle cabin in a door closed state, and locations that can be seen in a door closed state are avoided. Namely, the reinforcements are not fastened using bolts at locations of the door inner panel that are exposed to the vehicle cabin inside (including end portions at the vehicle cabin inside of the bead portion) at locations further to the vehicle width direction inside than a weather strip in the door opening in a door closed state. Thus, according to such technology, it is difficult to ensure a rigid fit of a back door while suppressing an increase in mass.